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Thread: A New Method for Increasing the Efficiency of a PCP

  1. #11
    Moderator rsterne's Avatar
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    I rebuilt the first gun (2260/Disco) I converted to the SSG today, using the last drawing in the post above.... It uses a much shorter spring guide that moves with the hammer, so the energy is not wasted.... Here are the two types.... I stole the spring from the top one for the new one, on the bottom....



    The top one has a long guide that stops when the rear nuts hit the gap adjusting bolt.... The bottom one has a sliding aluminum collar that pushes against the end of the gap adjusting bolt when you cock the gun.... and the stop nut slides back inside the adjusting bolt.... When you fire, the guide accelerates with the hammer, and just before it hits the valve, the stop nut hits the collar and carries the collar with it.... All the moving parts provide their energy to the valve.... The gap adjusting nut must be larger in diameter to allow the stop nut to pass through the center when the gun is cocked.... The collar is centered in the front of the end plug, which keeps everything aligned.... You can see how much shorter the new setup is than the original, and when cocked, the stop nut stays inside the gap adjusting bolt, as in the photo below....



    The photo above is with the gun cocked.... Compare that with the photo below of the original SSG setup, also with the gun cocked....



    There is no longer a pinch point to worry about, and it looks MUCH nicer and more compact....

    How does it work?.... FABULOUS !!!.... When I first assembled it, I used 0.1" less preload than I did in the original version, because I expected a stronger hammer strike and I didn't want to go past where I wanted to end up.... Well, it turned out I should have reduced the preload by 0.2", because I had more velocity than I wanted from the heavier hammer strike.... When I cranked it up (with no gap) it was well over 1000 fps with Kings, and I just happened to have some of the new 34 gr. King Heavies here, so I tried them.... With a minimum gap I was in the mid 800s, which was 55 FPE, compared to the best I could do with the old SSG with the Kings of 50 FPE.... So, I pulled it apart, increased the preload to maximum with the 2200 spring, and was rewarded with even more velocity.... By maxing out the spring to coil bind (preload, no gap), I hit 948 fps (68 FPE), which is harder than this gun has ever shot before.... Once I backed it out to get a tiny gap, it was shooting right at about 900 (62 FPE), but it was using a lot of air, so I backed it out another turn, and settled for a peak velocity of 880 fps with a 5-shot string from 2000 psi down to 1300.... The average was 866 fps (57 FPE), at an efficiency of 1.30 FPE/CI.... which is pretty astounding for a mildly modded Disco with the small tube from a 2260....

    I really like this version of the SSG, particularly for guns where you need lots of hammer strike to get the dwell for high power with heavy pellets.... It still has the advantage of eliminating hammer bounce, but it doesn't waste the energy the spring puts into the guide, instead it uses the weight of the guide to increase hammer strike and dwell.... In addition, it is much more compact, and the guide can be hidden inside the adjuster, providing the hammer stroke isn't too long (this gun is 0.65").... All in all, I think it's a significant improvement over the original.... particularly for higher powered PCPs....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  2. #12
    Moderator rsterne's Avatar
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    I pulled apart my 2560 today and swapped it over to the new style one with the internal stop.... Here are the old and new parts....



    I am now using a 10-32 machine screw with a piece of 7/32" OD tubing slid onto it for the guide.... Then you slide on the spring and an aluminum collar that hits the end of the gap adjusting bolt when cocking the gun and compresses the spring.... The stop nut is turned from a piece of 5/16" rod, drilled and tapped 10-32 and tightened against the end of the brass tube.... I start out a bit longer than I need and keep shortening the tube until I can get the gun shooting on the plateau with no gap.... Once I get the right length, I install the stop nut with a drop of blue Loctite, tightened against the end of the tube.... The stop nut has a slot in the end for this purpose.... The gap adjusting nut is drilled just over 5/16" because the stop nut has to slide through it.... The end cap is tapped 7/16"-20NF for the adjusting bolt, and then counterbored just over 7/16" to miss the cocking collar.... At the bottom of the photo is the original SSG I made.... You can see how much shorter the new guide is.... Below is the new SSG assembly, ready for installation....



    When the gun is uncocked, the stop nut is recessed about 1/2" inside the gap adjusting bolt, so you can't see it.... Compare this with the one above, where the stop nut and bumper O-ring (no longer required) are outside the gap adjusting bolt.... Below is what the gun now looks like when cocked....



    This installation is much cleaner, and there is no way you can pinch your fingers like could happen with the old one.... However, you still have a cocking indicator because the stop nut (the part with the slot) is visible when cocked.... With no gap I had about 985 fps, which I could adjust down to whatever I wanted.... At 1-1/2 turns out the velocity was just over 900 fps and the gun was very quiet.... I ended up about 1 turn out, with a average velocity of 960 fps, the same as I had before.... I might have lost a couple of shots compared to the first SSG, but I have still gained about 40% more shots per fill than without the SSG.... and I no longer have to worry about pinching my fingers and I can wrap my thumb over the wrist of the stock again because is it so much more compact.... The efficiency is around 1.40 FPE/CI....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  3. #13
    Moderator rsterne's Avatar
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    I was curious what I could get for efficiency using the SSG.... so I took my 2260 HPA, which is regulated at 1600 psi, and started dialing back the power and recording the pressure drop for 20 or 30 shots, using 18.1 gr. JSBs.... Here is what I came up with....



    This is the first time I have had an efficiency greater than 2.0 FPE/CI.... At just under 12 FPE, I got 2.12 FPE/CI, which is 7.7 barcc/FPE.... That would give me 250 shots per fill on the 13 CI tank.... Adjusted for 23 FPE, the efficiency would be 1.7 FPE/CI and 100 shots per fill.... The way the gun is normally tuned, at 37 FPE, I can actually shoot down to 1400 psi without velocity drop, and I get 60 shots (6 mags.)....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  4. #14
    Moderator rsterne's Avatar
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    For some time I have been wondering how effective the SSG would be on a CO2 gun like the Crosman 2260.... I had the opportunity to try that out today.... The testing started out with the gun configured exactly as a stock 2260.... Stock valve, hammer and spring, stock transfer and barrel ports, and a 24" barrel, although the gun did have a Crosman steel breech on it.... I loaded a brand new 12 gr. CO2 cartridge, fired the gun twice to pierce the cartridge, and then shot a string using 18.1 gr. JSB Heavy pellets until the velocity dropped to 300 fps, at which point I stopped.... I fired one shot every 30 seconds, and the temperature was 68*F.... I then repeated the testing using a much lightened hammer that was 50% of the weight of a stock one.... In both cases the stock rear cap was in place, so the preload on the 2260 spring was completely stock.... I then fitted an SSG, using the same spring, with as much preload I could use and still cock the gun with no gap between the end of the guide and the hammer.... I adjusted the gap to 0.020", installed a new cartridge, fired two shots to pierce it, and then fired another string.... The results are shown in the graph below....



    There are some interesting things to note.... In stock form, even though I was only shooting every 30 seconds to limit cooling, the velocity declined in a near linear fashion for 30 shots, and then dropped rapidly, with a total of 37 shots above 300 fps.... I calculated the FPE of every shot and added them up, getting a total of 341 FPE from a 12 gr. cartridge.... With the lighter hammer, the initial velocity was lower, but within 15 shots it leveled off, staying within a very narrow ES for another 30 shots before dropping, with a total of 53 shots above 300 fps.... The total FPE from that cartridge was 457 FPE, which is pretty good, and a 34% improvement over stock.... With the light hammer and the SSG, the velocity stabilized quite quickly, and I got over 60 shots before it started to decline.... and the initial decline was not as dramatic.... and I got a total of 78 shots above 30 fps.... over twice as many as stock.... The total FPE from a cartridge with the SSG fitted was 627 FPE, breaking my own previous record of 608 FPE with an 18" barreled 1750.... That represents 84% more energy from a 12 gr. than I got stock....

    I am extremely pleased with the huge increase in FPE per 12 gr. CO2 obtained by using the SSG.... This was, additionally, the first attempt using an SSG on a CO2 gun for me, and breaking the 600 FPE mark without tuning was pretty impressive.... I look forward to trying some different settings to see if I can get even more energy from a 12 gr. in the future.... but right off the bat, we know it works great on CO2....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

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